The invention resides in a method for controlling the NOx concentration in the exhaust gas of an internal combustion engine wherein, based on an NOx control error or deviation, a control value is determined for adjusting the NOx concentration.
For maintaining the legal NOx emission limit values of an internal combustion engine, the internal combustion engine is operated in a controlled manner. DE 103 33 933 A1 discloses a particular method and arrangement for achieving this task. In this method first an NOx control error or deviation from a desired NOx value is determined. Based on the determined NOx control error a controller determines a control value. Then via a performance graph, an exhaust gas flow rate is assigned to the control value. In addition, a logic is provided which examines the emissions based on the particle control deviation and the NOx control deviation. Upon determination of a deviation from the optimum values the logic causes the controller to control or adjust the respective control device by adjusting the respective control value. In this method, it is however possible that a certain control deviation remains in effect.
It is therefore the principal object of the present invention to provide an NOx control circuit which optimizes the control quality.